/Engine/Plugins/Runtime/MeshModelingToolset/Source/ModelingComponents/Public/Selection/GroupTopologySelector.h
Using the edges in the given selection as starting points, add any "edge loops" containing the edges. An edge loop is a sequence of edges that passes through valence-4 corners through the opposite edge, and may not actually form a complete loop if they hit a non-valence-4 corner.
true if selection was modified (i.e., were the already selected edges part of any edge loops whose member edges were not yet all selected).
bool ExpandSelectionByEdgeLoops ( [FGroupTopologySelection](API\Plugins\DynamicMesh\FGroupTopologySelection) & Selection )